In order to maintain heat-insulation performance of vacuum heat-insulation materials for a long period of time, it is required that films having excellent gas-barrier properties are used in shell materials so as to prevent penetration of outside gases into the vacuum heat-insulation materials, thereby maintaining vacuum states inside the vacuum heat-insulation materials.
For the above purpose, films including metal foils such as aluminum foils have been employed for shell materials in conventional arts. However, when such films including metal foils are used for vacuum heat-insulation materials, penetration of heat through metal foils (so-called “heat bridge”) is caused, and thus, there is a problem in which expected heat-insulation performance is not obtained.
To solve such phenomena of heat bridge, methods in which stainless-steel-foil layers, ceramic-vapor-deposited-film layers, aluminum-vapor-deposited-film layers, or the like that have comparatively small heat conductivity are used as barrier layers, instead of using aluminum-foil layers, have been known.
Furthermore, as disclosed in the publication of Japanese Patent No. 4,649,969, there is also a method in which, in consideration of realization of sufficient gas-barrier properties and prevention of heat bridge phenomena, a laminate film that includes an aluminum-foil layer as a component layer and that serves as a gas-barrier layer is used for at at least one of the shell materials present at the front and the back of the vacuum heat-insulation material. As another example, there is a method in which a laminate film that includes, as component layers, at least two barrier-film layers including multiple inorganic-oxide-vapor-deposited layers serving as gas-barrier layers is employed as a shell material can be mentioned.